With all 3,630 precincts reporting, Kloppenburg received 740,090 votes, while Prosser received 739,886.

The race reflected the divide in the state over Republican Gov. Scott Walker’s collective bargaining law, which would eliminate public workers of nearly all their union powers. The issue, which could ultimately be decided by the state Supreme Court, propelled the relatively unknown Kloppenburg into prominence and heightened voter interest in the election.

Kloppenburg, an assistant state attorney general, began her campaign with almost no name recognition and faced long odds against Prosser. The 12-year Supreme Court veteran emerged from a nonpartisan February primary with 55 percent of the vote, while Kloppenburg finished second out of four candidates with just 28 percent.

But opponents of the collective bargaining law redefined the Supreme Court race as a referendum on Walker and all Republicans, working to leverage the anger over the measure against Prosser, a former GOP legislator. They branded him a Walker clone and held Prosser up as the best hope for stopping the measure.

Prosser’s campaign didn’t immediately return a message early Wednesday. However, the Milwaukee Journal-Sentinel reported that he told supporters at his election-night party that there was "little doubt" there would be a recount. Kloppenburg told supporters she hadn’t given up.

"We’re still hopeful," Kloppenburg said. "So thank you all and let’s all get a good night’s sleep and see what tomorrow brings."

Walker has insisted the new law is necessary to help balance the state’s budget, but Democrats see it as a direct assault on unions, a key campaign supporter for the party.

Tens of thousands of people spent weeks protesting the measure at Wisconsin’s Capitol and Democrats in the Senate even fled the state to try to block a vote in that chamber. Walker eventually signed the bill anyway, but the measure is on hold as legal challenges wend their way through the courts. Sixteen state senators - eight Republicans and eight Democrats - face recall efforts over the proposal.

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The measure’s opponents ultimately hope a Kloppenburg upset would tilt the Supreme Court’s ideological balance to the left and set the stage for the court to strike the law down. A legal challenge already is before the court, although the justices have not decided whether to consider it. They also want to show the Republican senators facing recalls that they’re next to go.

Prosser pushed back, disavowing his GOP connections. He accused pro-labor groups of hijacking the race and argued Kloppenburg was so closely tied to them she couldn’t ethically rule on the law.

Interest in what would have been an otherwise sleepy race skyrocketed.

According to the Brennan Center for Justice, a New York University program that tracks spending on judicial races, outside groups, including the Tea Party Express and national labor organizations, had poured a record $3.5 million into race through Monday.

Statewide voter turnout in Tuesday’s election was 33 percent, shattering state election officials’ pre-election predictions of 20 percent. April elections in past years have seen turnouts ranging from 18 percent to 21 percent.

Deborah MacFarland, 67, and her husband, Robert, 69, of Bayside, said the issue helped persuade them to vote for Kloppenburg.

But Kelly Bodoh, 37, a self-described Libertarian from Sun Prairie, picked Prosser, saying she was upset that Democratic senators fled the state.

"The way the past couple of months have gone down in Madison made me very distrustful of that faction," she said. "Emotions and disrespect ruled the response to the ... bill."

Walker has said he wouldn’t interpret the election results as either an endorsement or indictment of his policies.

Wisconsin law does not provide for automatic recounts. Instead, candidates have three days after official results are tallied to request one. They must provide a specific reason for such an effort to state election officials, such as a mistake in counting or some other irregularity.